In order to produce a truly effective string or cord repair (we will refer to it only as a cord repair), a number of conditions must be met. First, the cord must have enough body adequately to fill the cut or puncture being repaired. Second, the cord body must be sufficiently limp and pliable to adapt itself to the shape of the puncture but yet still be strong enough to withstand the stress of being jammed into the puncture by the applicator tool. Third, the adhesive which impregnates the cord must be sufficiently distributed throughout the puncture and the fibrous body to prevent air leakage at any point. A fourth requirement is that there be no free path of air to seep through the core of the cord (where the adhesive may not have fully penetrated) from inside the tire to the outside. A fifth requirement is that the adhesive must be insoluble in oils or gasoline to which the tire may be subjected in normal use. Also the adhesive must not be free to migrate under normal conditions of heat and stress encountered in use, but yet the adhesive must be capable of adapting to the shape of the puncture as well as achieving intimate and complete adhesion with the walls of the entire puncture.
These criteria are difficult to meet simultaneously. Thus, if a sufficiently strong fibrous body is provided to withstand the stress of insertion, the matting of the fibers thereof not only renders thorough impregnation with adhesive extremely difficult but also tends to make the body relatively stiff so as not to yield into conformance with the shape of the puncture. Also, if a non-vulcanizable elastomer is used which is capable of migrating so as to fill the entire puncture, the elastomer will thereafter be washed out by oil or gasoline rendering the repair ineffective. Conversely, if a vulcanizable elastomer is employed it must be vulcanized or else it too will wash out, but if it is vulcanized, then it will tend not to yield completely to fill the puncture, especially if the puncture has an odd shape.
Another problem with cord repairs is that the size and shape of punctures cannot be predicted. One way previously used to deal with this problem has been to use a reaming tool so as to increase the size of small punctures to a larger, standard sized hole suitable for a given large sized cord. Such reaming, however, ruptures the reinforcing within the tire and is generally undesireable. Repairing still larger sized cuts or punctures by using several cord repairs placed side-by-side in the puncture has been attempted, but it is considered risky because the adjacent previously vulcanized cords are not intimately adhered to each other.
It is, therefore, a general objective of this invention to provide cord repair material which satisfies the foregoing criteria and effectively deals with each of the problems arising therefrom. More specifically it is an object of the invention to provide a cord repair material which can repair punctures of a wide range of sizes and shapes and do so without at the same time requiring any reaming for small holes. Another object is to provide a strong cord body but yet to combine it with a vulcanized elastomer in such a way that no seepage of air can take place through the core of the cord. Still another object is to provide a vulcanized elastomer for such a cord, which elastomer, although vulcanized, can yield sufficiently completely to fill punctures of any shape.